The Royal Parks has warned it will refuse to approve the Mayor’s preferred route on Birdcage Walk in St James’s Park — forcing cyclists to instead use an unprotected route via Horse Guards Road that crosses two dangerous junctions on The Mall.

In her formal response to a Transport for London consultation, Royal Parks chief executive Linda Lennon said building a cycle superhighway on the north side of Birdcage Walk would “impede access” to a works yard, interfere with “cleaning/tree maintenance operations” and “significantly affect day-to-day park operations”.

She continued: “A suitable method of separation [of cyclists from vehicles] has not been presented to the Royal Parks to enable this proposal to work satisfactorily.”

This follows the Royal Parks’s refusal to allow the route to pass in front of Buckingham Palace — a plan TfL has had to shelve due to lack of support.

Construction began last month on other sections of the £47 million scheme, linking Acton and Tower Hill, with completion due by next May.

But unless the stand-off with the Royal Parks is resolved, the superhighway will have a sizeable gap where cyclists are not protected from vehicles.

Ms Lennon said the Royal Parks “supports the overall ambition” of the Mayor’s east-west “Crossrail for cyclists” scheme but said “technical, operational, safety and engineering challenges are still to be resolved”.

Routes used by cyclists in Kensington Gardens and Hyde Park — such as Rotten Row — already suffer from “challenging conflict issues with pedestrians and animals”. Royal Parks managers are concerned that the superhighways will increase the danger to non-cyclists.

Ms Lennon said: “The Royal Parks reserves the right to re-site, reconfigure or remove these routes and infrastructure in future if the impact of the cycle routes lead to increased conflict, undermines safety or has a detrimental impact to the intrinsic qualities of other areas of the park.”

A Royal Parks spokesman said it backed the route via Horse Guards Road and The Mall as “the best for a continuous cycle route that links the cycle superhighway”.

Alan Bristow, director of road space management at TfL, said: “We recently consulted on a segregated two-way cycle track on Birdcage Walk, providing cyclists travelling to and from Victoria with a route protected from vehicles.

“We will continue to work closely with the Royal Parks as we finalise detailed plans for the east-west route through St James’s Park.”